President Joe Biden referred to Russian President Vladimir Putin as a “crazy SOB” on Wednesday, which incurred a strong response from the Kremlin.

The two leaders often engage in tough rhetoric toward one another, though these comments come in the aftermath of the death of Alexei Navalny, Putin’s main opposition leader in Russia. Biden argued last week that Putin was responsible for Navalny’s death, while the United States is set to unveil new sanctions against Russia on Friday.